Characterisation and identification of sediments in shallow water by means of high frequency acoustic remote sensing Steve Vandenplas This doctoral project fits within the scope of scientific research in order to gather in a reliable and accurate way information about the structure and the morphology of the sea floor. The actual commercially acoustical measurement instruments can only provide empirical based information about the nature of the sediment layers. An inverse procedure based on a maximum likelihood estimator is used to estimate the physical parameters of sediments. The estimated geo-acoustical properties of marine deposits (sediment characterisation) from acoustical measurements depend strongly on the validity and accuracy of the models used for the acoustical wave propagation in the marine environment. Different models for the wave propagation through the sediments are proposed and compared, and their geo-acoustical parameters are estimated. The sea floor, as an acoustical system, is complex and its properties vary often randomly in space and time. Model errors are inevitable and obtaining accurate and proper back scattered sea floor data is difficult. That's why the wave propagation models and the inverse procedure are first studied and validated in the laboratory. Transmission and reflection experiments are performed under normal and oblique incidence. Beam spread correction is taken into account. Next, the inverse procedure is applied on back scattered signals from the sea floor. This project could lead to a powerful measurement system, which will be of great benefit to many companies and public services: dredging companies, navy activities (mine detection), police services (environmental pollution), among others. Further research interests are also bounded beam propagation and decomposition models.